At the present time the enforcement of vehicle speed limits is based primarily on the intervention of police officers. For example, a police officer in a car will observe the speed of a suspected speeding car by following the speeding car and monitoring the officer's speedometer. Alternatively, a police officer on the side of the road, or in his car, will detect and record the speed of a moving vehicle using radar, such as Doppler radar, or a laser beam, or sensing coils on the roadway, as in U.S. Pat. No. 4,234,923.
The control and reduction of speed limit violations is both a safety and traffic issue. It is believed that the number of highway accidents may be reduced if motorists obey the speed limits, or at least keep their speeds to no more than 10 miles above the limits. If more drivers drove at safe and legal speeds, the number of motor vehicle collisions, and associated injuries and fatalities, would be reduced. If the number of highway accidents may be reduced, the savings in medical expenses and car repair expenses would be enormous. In addition, traffic accidents are a major cause of traffic congestion, since blocking one of three lanes of a highway due to a traffic accidents may reduce the highway capacity by 50 percent.
In addition, it has been suggested, at least in the patent literature, that vehicle speeds may be automatically monitored and a photograph taken of those vehicles which exceed the speed limit, as in U.S. Pat. Nos. 4,866,438 and 5,066,950. Those systems require a matching of the photograph of the license plate number with a list of license plate numbers and mailing the traffic violation ticket to the owner of the vehicle. That system is not legally acceptable in many states, since there is no human witness of the traffic violation and the owner of the vehicle may not be the one driving at the time of the speeding violation.
In U.S. Pat. No. 5,231,393 entitled "Mobile Speed Awareness Device", the speed of a vehicle is detected by a radar gun. The vehicle speed is displayed on a lighted number display board mounted on a trailer.
In U.S. Pat. No. 5,204,675 an automatic toll collecting system obtains vehicle identification from a vehicle number plate and calculates the toll based on the number plate.